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Clutter is a technology developed by Microsoft for its Outlook email client that helps users automatically organize their Outlook inboxes and prioritize important e-mails by moving lower priority messages to a new Clutter folder.

The Microsoft Clutter technology debuted in late 2014 for Office 365 users, and is now available on Outlook PC and mobile applications as well as the Outlook Web App.

Clutter is designed to learn from a user’s choices and actions to better determine which messages are more likely to be ignored by the user as they come in. These messages end up in the Clutter folder.

Clutter vs. Anti-Spam Filters, Junk Mail and Outlook Rules

Clutter operates in a fashion similar to third-party anti-spam filters like Cloudmark or Spam Bully, in that it learns how to filter out lower priority mail based on a user's reading habits and actions.

Clutter does differ from two other built-in Outlook features, Junk Mail and Rules, that might at first seem similar in nature to Clutter. The Junk Mail feature in Microsoft Outlook processes messages based on a massive collection of known spam that Microsoft has identified over time. This junk mail processing is generic in nature, as opposed to the more personalized approach taken by Clutter.

Clutter differs from Outlook Rules in that rules are defined by the user and take priority over Clutter processing. There are also significantly more options and actions available through Microsoft Outlook rules than with Clutter.

In terms of message processing priority, Outlook will take the following steps in order:

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